a chip on your shoulder

a chip on (one's) shoulder

An attitude that leads one to become combative or easily angered. Fred has such a chip on his shoulder—you never know what's going to set him off next. She won't admit it, but Kate has a chip on her shoulder when it comes to discussing her career. She was an enthusiastic player when she first started, but she seems to be getting a chip on her shoulder from dealing with all of the politics within the professional league.

a chip on your shoulder

a strong and usually long-standing inclination to feel resentful or aggrieved, often about a particular thing; a sense of inferiority characterized by a quickness to take offence. informal

In 1830 the Long Island Telegraph described the practice which gave rise to this expression: ‘When two churlish boys were determined to fight, a chip would be placed on the shoulder of one, and the other demanded to knock it off at his peril’.